1. Field of the Invention
This invention relates to a windshield antenna for an automotive vehicle, particularly to a layout or an arrangement of the antenna.
2. Description of Prior Art
Conventionally, an automobile has an antenna to receive signals of radio broadcast wave, such as frequent modulation wave (FM) or amplitude modulation wave (AM). When the automobile is running in mountain areas or in city areas crowded by high-rise buildings, a radio wave receiver in the automobile causes a noise by steep fluctuation of electrical wave field or a multipass distortion especially in case of FM radio waves. One effective way to resolve such a problem is to install a plurality of antennae on the vehicle body and to select and connect the most suitable or sensitive antenna to the radio broadcast receiver. This method is generally known as a so-called diversity receiver system.
In view of the sensitivity of antennas, a pole antenna is more preferable than other antennas to install on the vehicle body; however, to build many pole antennas is not desirable in view of the design or layout of vehicle body. In such a case, there has been used a windshield antenna array which has antenna wires located on the windshield glass. For example, Japanese Laid-open Utility Model Application 58-61509 shows windshield glasses having windshield antennas at opposite rear sides of the vehicle body, and proposes to select one of two antennas for the diversity receiver system.
It is also well known that the characteristic of an antenna is determined by the length of the antenna, that is, its most sensitive band is limited in a particular frequency zone or band. In other words, a predetermined length antenna has an inherently low sensitivity characteristic with respect to other particular frequency zones or bands.
Such an antenna characteristic does not affect the performance of radio so much in case of using a pole antenna. However, in case of using a windshield antenna, this characteristic causes the problem that the radio cannot receive sufficient gain in a particular frequency zone or band, which results in inconvenience in receiving radio broadcast waves steadily.
One practical way to resolve this problem is to provide a plurality of antenna wires which have different lengths so as to provide a wide range and highly sensitive receiving characteristic. But, if these different length antenna wires are disposed in parallel on the windshield glass end, the antenna wires terminate in different positions in the longitudinal direction at some intervals. Particularly, shorter antenna wires look like they were cut off prematurely. As a result, the windshield antenna becomes unattractive.
The purpose of the present invention is to provide different length windshield antennas for realizing the wide range and highly sensitive receiving characteristics without losing attractiveness and with keeping the good look of the windshield glass.